As few as four senators who between them secured fewer than 10,000 votes could decide whether Australia goes to an early double dissolution on July 2 or waits for a standard spring poll, after Malcolm Turnbull arranged for an emergency re-call of Parliament to test their resolve.

Daring the Senate to block his government's building unions watchdog bill for a second time, and another union-corruption bill for a third time, thus sending the nation to a winter double dissolution election, he said "the time for game playing is over".

The stunning tactical ambush not only upped the stakes, it caught the entire political establishment off-guard on Monday, including Mr Turnbull's own MPs and even inner-circle ministers as senior as his Treasurer, Scott Morrison.

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Australian voters must now brace for what will feel like an election campaign extending for a staggering 15 weeks.

Prime Minister Malcolm Turnbull on Monday.Credit:Andrew Meares

The Prime Minister used a snap press conference in Canberra to reveal he had visited the Governor-General Sir Peter Cosgrove and advised him to prorogue the Parliament - officially ending the current session - before also using the Governor General's powers to recall both houses to sit for three weeks from April 18, ahead of a re-scheduled May 3 budget.

The move, which relied on the little-used provisions set out in section 5 of the constitution, means the seven-week pre-budget parliamentary break leading up to the scheduled May 10 budget has been halved with the special sitting dedicated entirely to consideration of a once-defeated bill to re-establish the Howard-era Australian Building and Construction Commission and the already twice-defeated registered organisations bill.

Both bills have come up against stiff Senate opposition from Labor, the Greens, and six of the eight cross benchers, almost all of whom were elected in 2013.

Passing them - both articles of faith for the conservative pro-Abbott wing of the party - would be a major win for Mr Turnbull's internal prestige. But their rejection would be even more advantageous, allowing him to run a full-throated anti-union militancy campaign in which he would attempt to paint Labor's Bill Shorten as a fellow traveller.

Prime Minister Malcolm Turnbull Credit:Andrew Meares

Mr Turnbull's action follows last week's successful passage of changes to Senate voting procedures which ended elaborate and opaque preference deals, and will almost certainly mean fewer independent and minor party senators will be elected in future.

The bold manoeuvre means that the independents and micro-parties must now decide between standing their ground on principle, which will cause the legislation to fail, prompting a double dissolution election in which most will lose their $200K jobs, or switching to support the bills. However a complete about-face would suggest their principles are worth less to them than their six-year sinecures.

Illustration: Ron Tandberg

Asked how long he had been planning the move, Mr Turnbull said: "well I've been aware of Section 5 of the constitution for quite a long time and the decision to proceed with this advice to the Governor-General, the final decision to do that, was taken last night [Sunday] ... if we do proceed to a double dissolution, the election will be on Saturday the 2nd of July".

In a further sign of the haste and need-to-know basis of the announcement, Treasurer Scott Morrison was forced to admit he had not known of the decision - including the crucial aspect in which the budget is brought forward to May 3 - when he was on Sydney radio just minutes before it became public.

"May 10, May 10," he told 2GB's Ray Hadley at 9.30 am, when asked about its possible rescheduling.

"We're preparing for May 10 Ray, I can't be clearer than that."

Uncertainty over the budget timing and the election itself has now been reduced to a choice between a dissolution of both houses for a July 2 election if the Senate remains obstructive, or the standard House of Representatives and half-Senate election due in the ordinary course of events in the September-November period anyway.

Buoyed by improving opinion polls, Opposition Leader Bill Shorten displayed little reluctance to ratchet-up his campaigning intensity accusing the Mr Turnbull of "playing election games" while declaring the difference between the Liberals and Labor "could not be starker".

"I challenge Malcolm Turnbull to get out his office and listen to what people have to say about his plans to gut Medicare and his plan to give big multinationals a tax cut," he said, ahead of a two-day swing through Queensland, the state where the election could be decided.

Four senators - Ricky Muir, John Madigan, Jacqui Lambie and Glenn Lazarus - received only 9901 individual primary votes in total; Madigan at the 2010 election, the rest at 2013.

Among the crossbench senators who opposed the bills in the past are Victoria's Ricky Muir, who secured 479 primary votes in 2013; John Madigan, who scored 1151 in 2010; Jacqui Lambie who secured 1501 in 2013; and the former League star Glenn Lazarus who did better with 6770.

Senator Lazarus has vowed not to support the ABCC bill in its current form, and Senator Madigan has flagged a similar intention, declaring he does not respond to bullying.

Senator Muir said the ABCC bill deserves a full debate and discussion around extending its powers to employers, adding it would be a "sad day in Australian democracy if we all folded and voted for the government, because they actually put a gun to our head".

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However, support could also come from others such as WA's Zhenya "Dio" Wang, and SA's Nick Xenophon.